This application relates to and claims priority, under 35 U.S.C. xc2xa7119, from German Patent Application No. 197 21 962.4, filed on May 20, 1997, and German Patent Application No. 198 08 106.5, filed on Feb. 26, 1998, the entire contents of both German Patent Applications hereby being incorporated by reference herein.
1. Field of the Invention
The present invention generally relates to an apparatus and a method for producing a one-part vehicle wheel with a hub and a rim.
2. Discussion of Background
It is known to manufacture vehicle wheels by casting. Compared with a cast workpiece as such, a higher strength can be obtained if a blank is shaped in a drop forge and is then further worked on a flow-forming machine. Such known methods are complicated and costly as a result of the tools required.
An object of the present invention is to provide a method and an apparatus with which it is possible to produce, simply and with high strength, vehicle wheels.
According to the present invention, the above-stated object is achieved by a method for the production of a one-part vehicle wheel having a hub and a rim, wherein: an undercut-free, substantially disk-shaped pre-form is cast; immediately following casting the pre-form is transported to a flow-forming machine, while maintaining a residual heat and is fixed therein; the fixed pre-form is split in its circumferential area and by subsequent spinning and flow-forming is shaped to an intermediate form with a rim base area, which already substantially has the wall thickness of the rim of the finished vehicle wheel; the intermediate form is cooled; and the cooled intermediate form is sized and end-worked to produce the finished vehicle wheel.
The design of the pre-form, as a substantially disk-shaped, undercut-free workpiece, makes it possible to use a simply constructed casting tool. Instead of a usually necessary, multi-part segmental tool, it is possible to use a simple, two-part casting tool. It is also possible to obviate the complicated removal of cast seams, which are unavoidable in multipart tools. The central area of the cast pre-form substantially corresponds to the hub of the finished vehicle wheel.
A simplification of the manufacturing process, accompanied by significant energy saving, results from the immediate transportation of the cast pre-form to the next working step on a flow-forming machine. After casting, the pre-form has a temperature of approximately 300xc2x0 C. Particularly when using light metals, it is advantageous, for avoiding cracks, to carry out flow-forming at an elevated temperature, which is preferably above the re-crystallization temperature of the material. During flow-forming of a heated pre-form, the forming forces required are much lower than with workpieces at room temperature.
Compared with the hitherto known methods, in which the rim contour and wall thickness are provided with a certain allowance for the final mechanical machining, in the method, according to the present invention, following calibration, the rim base and lateral rim beads are substantially end-shaped. For the lateral areas and the formation of bores, a certain metal-removing working is required.
The method, according to the present invention, is advantageously further developed in that the pre-form, after casting and prior to shaping to the intermediate shape, is supplied with additional heat. For example, the pre-form is heated to approximately 400xc2x0 C. in a furnace, which the pre-form passes through on conveyance from the casting equipment to the flow-forming machine. In the furnace, it is merely necessary to heat from the temperature after casting to the desired machining temperature during flow-forming. Compared with heating which is started from room temperature, this leads to shorter warm-up times and an improved energy balance.
According to another variant of the present invention, the vehicle wheel is manufactured from a non-age-hardenable aluminum alloy, particularly, Gk-A1 Si 11 Mg. The intermediate form requires no additional heat treatment and can be sized directly after cooling. Cooling can take place in a tunnel-like cooling device, which the intermediate form passes through on conveyance to the sizing device.
An alternative variant comprises the vehicle wheel being manufactured from an artificially ageable aluminum alloy, particularly, Gk-Al Si 7 Ma Wa.
Such aluminium alloys can readily undergo non-cutting shaping. In order to obtain a desired strength, following the shaping of the intermediate form, a heat treatment is necessary.
The heat treatment preferably comprises the intermediate form undergoing a solution heat treatment and a quench cooling. The temperature control and duration of the solution heat treatment, as well as the speed during quench cooling, are dependent on the material used. The cooling normally, takes place to room temperature.
Another variant of the method, according to the present invention, comprises the sizing of the rim being performed by a section roller on a flow-forming machine and wherein the rim only mechanically undergoes end-working in its lateral areas at the rim beads. The section roller has a contour, which is the negative form of the desired contour of the rim base and rim beads. Thus, sizing can take place by a simple, radial infeeding of a section roller.
The above-described object of the present invention can also be achieved by a method for producing a one-part vehicle wheel with a hub and a rim, as follows. The circumferential area of a substantially disk-shaped pre-form is split a first time. By subsequent spinning and flow-forming an intermediate form is shaped with a radial flange and a rim base area, which already substantially has the wall thickness of the rim of the finished vehicle wheel. The radial flange is then split a second time into an outer leg and an inner leg directed towards the rim base. From the outer leg is finally shaped a rim bead and from the inner leg a roughly axially directed rim shoulder and an undercut is formed between the rim base area and the rim shoulder.
In a preferred method variant, by spinning and flow-forming, the rim bead is shaped from the outer leg and the rim shoulder is shaped from the inner leg.
Another advantageous method variant comprises a hump being shaped on the rim shoulder.
According to the present invention, an apparatus is provided for achieving the object, as follows. The undercut-free castings permit a simple, problem-free manufacture of preforms. Whereas complicated castings must initially be cleaned, in the case of the present invention, the simple parts can be directly supplied to a flow-forming process. During transportation, planned cooling and additional heating of the still-heated castings leads to a desired flow-forming temperature being obtained.